1. Field of the Invention
The present invention relates to a piezoelectric material. The piezoelectric material includes a lead zirconate titanate (hereinafter referred to as "PZT") ceramic, and a noble metal or a noble metal alloy which is added dispersedly in the PZT ceramic. Moreover, the present invention relates to a piezoelectric element. The piezoelectric element has a laminated structure of a PZT ceramic and a noble metal or a noble metal alloy, instead of a dispersion of a noble metal or a noble metal alloy which is dispersed as particles in the PZT ceramic.
2. Description of the Related Art
There is a piezoelectric material in which a noble metal is added to a PZT ceramic. Japanese Unexamined Patent Publication (KOKAI) No. 3-223,149 discloses one of the piezoelectric materials, a PZT ceramic to which silver (Ag) is added. However, Ag has a low melting point (e.g., 961.degree. C.), and is likely to be oxidized. Accordingly, Ag is solved in the PZT ceramic, or is turned into oxides. As a result, the piezoelectric material disclosed in the publication fails to effect the straining-ability upgrading mechanism which results from the dispersion of the noble metal particles.
Japanese Unexamined Patent Publication (KOKAI) No. 7-232,962 discloses a PZT piezoelectric material in which a powder of palladium (Pd), one of the noble metals, is added in an amount of from 0.02 to 0.4% by weight with respect to a PZT ceramic. Note that 0.4% by weight, the maximum content of the palladium powder, is equal to about 0.27 parts by volume with respect to the PZT ceramic taken as 100 parts by volume. However, in the PZT piezoelectric ceramic disclosed in the publication, the volume content of the palladium powder is extremely small. Consequently, the PZT piezoelectric ceramic can little effect the straining-ability upgrading mechanism which results from the dispersion of the noble metal particles.
Moreover, there is an integrally sintered piezoelectric element. In the integrally sintered piezoelectric element, a plurality of piezoelectric material layers and electrode layers are laminated one after another. Thus, the electrode layers are disposed in the integrally sintered piezoelectric element. As a result, the integrally sintered piezoelectric element can relieve the micro internal strains. However, the internal electrode layers have a heavy thickness of from 1 to 5 .mu.m, and exhibit an irregularity on the order of a few micrometers. When the internal electrode layers are flexible, they absorb the electric-field-induced strains which the piezoelectric material layers produce under a compressive load. Accordingly, the conventional integrally sintered piezoelectric element cannot exhibit the strain of its own. Moreover, when the irregulaity is present in the internal electrode layers, the irregularity absorbs the strains which result from the extending piezoelectric material layers. In this instance as well, the conventional integrally sintered piezoelectric element cannot effect its own abilities.